This invention relates to medical ultrasonic imaging systems, and in particular to methods for improving contrast and detail resolution in such systems.
In conventional medical ultrasonic imaging, beam signals are filtered with filters of different band passes, and the filtered beam signals are then combined, either before or after envelope detection.
In one approach described in Bolorforosh U.S. Pat. No. 5,891,038, assigned to the assignee of the present invention, the two beam signals are combined prior to envelope detection and then displayed. This operation is conventionally known as a synthesizing operation, and it can improve the spatial resolution of the resulting image signal in some situations. Alternatively, the filtered beam signals can be envelope detected prior to combination as described in Lizzi U.S. Pat. No. 4,531,019. This operation is commonly known as compounding, and it can improve the contrast resolution of the resulting image in some cases.
In these prior-art approaches, beam signals are either compounded for an image frame or synthesized for an image frame.
The preferred embodiments described below adaptively combine the information from two or more different beam signals characterized by different frequency bands. These two or more beam signals are combined prior to envelope detection in a synthesis operation, and they are also combined subsequent to envelope detection in a compounding operation. The compounded and synthesized beam signals are then weighted and combined to produce the image signal. The weighting factors are adaptively chosen to emphasize either the compounded beam signal or the synthesized beam signal, depending upon the currently prevailing beam signal characteristics. In this way, the synthesized beam signal can be made to dominate in regions of the image frame where improved detail resolution is important and the compounded beam signal can be made to dominate portions of the same image frame where improved contrast resolution is important. Alternative embodiments use the local intensity, variance, coherence factor, or signal to noise ratio of one or more of the beam signals to select the weighting factors.
The foregoing paragraphs have been intended by way of introduction, and they are not intended to limit the scope of the following claims.